1. Field of the Invention
The present invention relates to a method of processing a gaseous volatile organic compound, an adsorption and desorption apparatus, and a volatile organic compound processing system. The present application is based on Japanese Patent Application No. 2006-189516, filed Jul. 10, 2006, the content of which is incorporated herein by reference.
2. Description of the Related Art
In factories which use various types of volatile organic compounds such as toluene, xylene, or the like, treatment facilities are inevitably provided to process gases containing volatile organic compounds (gases to be treated). In such a facility, according to a typical method of processing a volatile organic compound, gas to be treated (or gas containing a volatile organic compound) is supplied to an adsorption and desorption apparatus where the volatile organic compound is adsorbed in adsorbent such as activated carbon, and the thus-adsorbed volatile organic compound is desorbed from the adsorbent with the aid of steam and then mixed in the steam. Thereafter, the steam mixed with the volatile organic compound is condensed, and the condensed water is distilled such that the volatile organic compound and the water are separated. Finally, the thus-obtained volatile organic compound is combusted and decomposed.
In such a conventional treatment method, in addition to the cost necessary for constructing/installing a treatment facility, the running cost of the facility also increases. To compensate for such inconveniences caused, a technique has been accordingly proposed for processing and decomposing a volatile organic compound, without incurring extra costs, by the use of an existing gas turbine provided in a factory (see, e.g., Japanese Unexamined Patent Applications, First Publications No. 2003-322324, No. 2004-036492, and No. 2004-184003).
For example, in the invention disclosed in Japanese Unexamined Patent Application, First Publication No. 2003-322324, a hazardous substance generated from a volatile organic compound is scavenged therefrom, and supplied to an air intake port of a gas turbine, and then compressed along with air in a compressor. The compressed air containing the hazardous substance is supplied to a combustor and fuel gas is concurrently supplied thereto, and they are combusted to thereby drive a turbine. The hazardous substance is combusted in the combustor and thus rendered harmless, and then discharged into the atmosphere together with exhaust gas of the gas turbine. In the meantime, in the inventions disclosed in Japanese Unexamined Patent Applications, First Publications No. 2004-036492 and No. 2004-184003, waste fluid containing a volatile organic compound is directly supplied to a combustor and fuel gas is concurrently supplied thereto, and they are combusted to thereby drive a turbine. The waste fluid containing a hazardous substance is combusted in the combustor and rendered harmless, and then discharged into the atmosphere together with exhaust gas of the gas turbine.
However, in the above-mentioned method of the volatile organic compound, in which the volatile organic compound is desorbed from the adsorbent with the aid of steam, part of the steam is condensed and becomes part of condensed water at the time of desorbing. Although the condensed water is discharged from the adsorption and desorption apparatus as drain water, a small amount of the volatile organic compound is contained or remains in this condensed water. To achieve a more complete process and decomposition of the volatile organic compound, it is necessary to decompose even the volatile organic compound contained in the drain water. As a concrete measure, it is necessary to separately or additionally provide a waste water treatment plant. This involves an inconvenience or increase of the cost of the facility. Especially, the larger the amount of the drain water, the larger the scale of the waste water treatment plant. That is to say, the larger the amount of the drain water, the higher the cost of facility.
The applicant consequently developed a technique to suppress or prevent such condensing of the steam, in which an adsorption and desorption apparatus to which compressed air is supplied is operated under high pressure. When the adsorption and desorption apparatus is structured such that it can endure such a high pressure, the wall thickness of a vessel of which necessarily becomes large. Accordingly, the heat capacity of the vessel is increased, so that rise in temperature thereof takes a long time at a heating process prior to a desorption process. When the heating process necessitates such a long time, to promote process efficiency, it is necessary to increase the capacity of the adsorption and desorption apparatus or to increase the amount of activated carbon (absorbent) used therein, thus resulting in an inconvenience or cost increase.